CN102365434B - Exhaust gas purification catalyst heating system - Google Patents

Abstract

The present invention provides a technology capable of reducing the amount of smoke generated in a temperature raising system that burns fuel added to exhaust gas flowing through an exhaust passage when the temperature of an exhaust purification catalyst needs to be raised. When the temperature of the exhaust purification catalyst (4) needs to be raised, bypass control is performed to cause the exhaust gas that bypasses the turbine (6b) to flow into the exhaust purification catalyst (4) via the bypass passage (7), and to perform fuel addition The valve (9) adds fuel to the exhaust gas flowing out of the turbine (6b) while causing the glow plug (10) to ignite the added fuel for fuel ignition control.

Description

Exhaust gas purification catalyst heating system

technical field

The present invention relates to a temperature raising system of an exhaust purification catalyst for purifying exhaust gas of an internal combustion engine.

Background technique

As a technique for raising the temperature of the exhaust purification catalyst of the internal combustion engine, an operation of raising the temperature of exhaust gas flowing into the exhaust purification catalyst may be performed. Patent Document 1 discloses a technique in which outside air is introduced into a combustion heater equipped with a fuel addition valve and an ignition device, and a combustion gas obtained by burning a mixture of outside air and fuel is guided to an exhaust purification catalyst.

Patent Document 1: JP-A-2002-47922

However, in a heating system that introduces external air into a combustion heater as in the above-mentioned prior art, the structure becomes complicated. On the other hand, the method of arranging a fuel addition valve and an ignition device in the exhaust passage upstream of the exhaust purification catalyst, and igniting the fuel added to the exhaust gas from the fuel addition valve so as to burn the fuel is very important for downsizing the temperature raising system. efficient. However, in this case, the higher the temperature of the air-fuel mixture to which the additional fuel is added, the higher the temperature of the combustion gas when the additional fuel is burned. Therefore, when the temperature of the air-fuel mixture is too high, a large amount of smoke may be generated and exhaust emission may be deteriorated.

Contents of the invention

The present invention has been made in view of the above-mentioned actual situation, and its object is to provide a temperature raising system that can reduce the amount of smoke generated in a temperature raising system that burns fuel added to the exhaust gas flowing through the exhaust passage when the temperature of the exhaust purification catalyst needs to be raised. Technology.

In order to achieve the above object, the temperature raising system of the exhaust purification catalyst according to the present invention adopts the following means.

That is, a turbine is provided in an exhaust passage of the internal combustion engine; an exhaust purification catalyst is provided in a portion of the exhaust passage on the downstream side of the turbine; a bypass passage connects the exhaust passage to the exhaust passage. A portion between the turbine and the exhaust purification catalyst is connected to a portion upstream of the turbine; and a fuel addition valve is provided downstream of the exhaust passage where the exhaust passage is connected to the bypass passage. The part between the side connection part and the above-mentioned turbine is used to add fuel to the exhaust gas flowing through the exhaust passage; The additional fuel added by the fuel addition valve is ignited; the first temperature increase control means, when the temperature of the exhaust purification catalyst needs to be increased, the first temperature increase control means makes the exhaust gas bypassing the turbine through the bypass passage flow into the In the exhaust purification catalyst; and a second temperature increase control means, when the temperature increase of the exhaust purification catalyst needs to be increased, the second temperature increase control means executes fuel ignition control, wherein the fuel ignition control is to make the fuel addition valve pair flow out from the turbine Add fuel to the exhaust gas, and make the ignition device ignite the added fuel.

In the above configuration, part of the exhaust gas discharged from the internal combustion engine flows into the bypass passage, and the rest flows into the turbine. Part of the energy of the exhaust gas flowing into the turbine is consumed by supercharging the intake air. Therefore, the temperature of the exhaust gas after flowing out of the turbine is lower than that before flowing in.

On the other hand, since the exhaust gas flowing into the bypass passage bypasses the turbine, it is introduced into the exhaust purification catalyst while maintaining a high temperature. In the present invention, when the temperature of the exhaust purification catalyst needs to be raised, the exhaust purification catalyst can be efficiently raised in temperature by allowing the high-temperature exhaust gas bypassing the turbine through the bypass passage to flow into the exhaust purification catalyst. Therefore, the amount of fuel added in the fuel ignition control can be appropriately reduced, and the amount of smoke generated can be reduced.

In addition, both the fuel addition valve and the ignition device are provided in a portion of the exhaust passage between the turbine and the downstream connection portion. The "downstream connection part" refers to a connection part located downstream of the turbine among the connection parts between the exhaust passage and the bypass passage among the exhaust passages. As described above, by arranging the fuel addition valve and the ignition device on the downstream side of the turbine, the temperature of the fuel gas during fuel ignition control can be appropriately lowered, thereby suppressing the generation of smoke.

In addition, the temperature raising system having the above configuration may further include an inflow ratio changing device capable of changing the bypass inflow ratio and the turbine inflow ratio, wherein the bypass inflow ratio is the amount of water flowing into the bypass passage. The turbine inflow ratio is the ratio of the amount of exhaust gas flowing into the turbine to the total amount of exhaust gas. Furthermore, the first temperature increase control means may control the inflow ratio changing device so that the turbine inflow ratio is larger than the bypass inflow ratio when the fuel ignition control is executed, and the inflow ratio changing device may be controlled so that after the fuel ignition control is executed, The bypass inflow ratio is larger than the turbine inflow ratio.

As a result, when the fuel ignition control is executed, since the amount of exhaust gas passing through the ignition device per unit time increases, the temperature of the combustion gas during the fuel ignition control can be lowered more reliably. On the other hand, after execution of the fuel ignition control, a larger amount of high-temperature exhaust gas bypassing the turbine can be introduced to the exhaust purification catalyst. Thereby, even after the execution of the fuel ignition control is completed, it is possible to continue raising the temperature of the exhaust purification catalyst.

In addition, means for solving the problems in the present invention can be used in combination as much as possible.

According to the present invention, it is possible to provide a technique capable of reducing the amount of smoke generated in a temperature raising system that burns fuel added to exhaust gas flowing through an exhaust passage when the temperature of an exhaust purification catalyst needs to be raised.

Description of drawings

1 is a diagram showing a schematic configuration of an internal combustion engine to which a temperature raising system for an exhaust purification catalyst in Embodiment 1 is applied and an intake and exhaust system thereof.

FIG. 2 is a graph illustrating a relationship between a glow plug (glow) peripheral gas temperature TGg and a smoke generation amount Qsm during fuel ignition control.

3 is a map illustrating the relationship between the inflow gas temperature TGc during bypass control and the required fuel addition amount Fur during fuel ignition control.

Fig. 4 is a flowchart showing a first temperature raising processing routine.

Fig. 5 is a flowchart showing a second temperature raising processing routine.

Fig. 6 is a flowchart showing a third temperature raising processing routine.

7 is a diagram showing a schematic configuration of an internal combustion engine to which a temperature raising system for an exhaust purification catalyst in Embodiment 4 is applied and an intake and exhaust system thereof.

Fig. 8 is a flow chart showing a fourth temperature raising process routine

Detailed ways

Hereinafter, referring to the drawings, examples of modes for implementing the present invention will be described in detail. However, unless otherwise specified, the technical scope of the invention is not limited to the dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment. Hereinafter, specific examples of the exhaust system of the internal combustion engine according to the present invention will be described.

<Example 1>

FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which a temperature raising system of an exhaust gas purification catalyst is applied and its intake and exhaust system in this embodiment. The internal combustion engine 1 is a diesel engine for driving a vehicle.

An intake passage 2 and an exhaust passage 3 are connected to the internal combustion engine 1 . A compressor 6 a of a turbocharger 6 is provided in the intake passage 2 . A turbine 6 b of the turbocharger 6 is provided in the exhaust passage 3 . An exhaust purification catalyst 4 is provided on the downstream side of the turbine 6 b in the exhaust passage 3 .

As the exhaust purification catalyst 4 in this embodiment, a DPNR (Diesel NOx catalyst) that supports an occlusion-reduction NOx catalyst (hereinafter referred to as "NOx catalyst") and oxidizes/removes fine particles such as coal in exhaust gas is used. Particulate NOx Reduction) catalyst. Here, the NOx catalyst has the function of storing NOx contained in the exhaust gas when the surrounding atmosphere is in a state of high oxygen concentration, and reducing the stored NOx when the surrounding atmosphere is in a state of low oxygen concentration and reducing components exist. . In addition, as the exhaust purification catalyst 4 , other catalysts such as selective reduction NOx catalysts or three-way catalysts having no NOx storage capacity may be used.

A portion of the exhaust passage 3 between the turbine 6 b and the exhaust purification catalyst 4 is connected to a portion upstream of the turbine 6 b via a bypass passage 7 . Furthermore, a bypass valve 8 capable of adjusting the cross-sectional area of the exhaust gas in the bypass passage 7 is provided in the bypass passage 7 . When the opening degree of the bypass valve 8 is changed, the amount of exhaust gas passing through the bypass passage 7 changes. Therefore, by changing the opening degree of the bypass valve 8, the ratio of the amount of exhaust gas flowing into the bypass passage 7 among the entire amount of exhaust gas discharged from the internal combustion engine 1, that is, the bypass inflow ratio Rbp, and the ratio of the amount of exhaust gas flowing into the bypass passage 7 to the total amount of exhaust gas discharged from the internal combustion engine 1 can be changed. The ratio of the exhaust gas amount of the turbine 6b, that is, the turbine inflow ratio Rtb. The bypass valve 8 in this embodiment corresponds to the inflow ratio changing device in the present invention.

Among the connecting parts between the exhaust passage 3 and the bypass passage 7, the connection part upstream of the turbine 6b is called "bypass branch part 3a", and the connection part downstream of the turbine 6b is called "bypass confluence part". 3b". When the bypass inflow ratio Rbp is equal to the turbine inflow ratio Rtb, the amount of exhaust gas flowing into the turbine 6b side in the bypass branch portion 3a is exactly equal to the amount of exhaust gas flowing into the bypass passage 7 side. Here, the sum of the bypass inflow ratio Rbp and the turbine inflow ratio Rtb is always 1.

In the present embodiment, a fuel addition valve 9 for adding fuel to the exhaust gas flowing out of the turbine 6 b is provided in a portion of the exhaust passage 3 between the turbine 6 b and the bypass junction 3 b. Furthermore, in the part between the fuel addition valve 9 and the bypass confluence part 3b in the exhaust passage 3, there is provided a valve that generates heat based on the power supply from a battery (not shown in the figure) and controls the fuel added from the fuel addition valve 9. A glow plug 10 for ignition. In this embodiment, the glow plug 10 corresponds to the ignition device in the present invention. On the other hand, the bypass confluence portion 3b corresponds to the “downstream side connection portion” in the present invention.

The part between the bypass confluence part 3b in the exhaust passage 3 and the exhaust purification catalyst 4, the peripheral part of the glow plug 10 in the exhaust passage 3, and the bypass valve 8 and the bypass valve in the bypass passage 7 The parts between the branch parts 3a are respectively provided with a first temperature sensor 11, a second temperature sensor 12, and a third temperature sensor 13 that output electrical signals corresponding to the temperature of the exhaust gas.

An electronic control unit (ECU: Electronic Control Unit) 15 for controlling the internal combustion engine 1 is provided in parallel with the internal combustion engine 1 . The ECU 15 controls the operating state of the internal combustion engine 1 and the like in accordance with the operating conditions of the internal combustion engine 1 and the driver's request. Moreover, in addition to the first temperature sensor 11 to the third temperature sensor 13 being connected to the ECU 15, various sensors for detecting the operating state of the internal combustion engine 1 (crank position sensor for detecting the rotational speed of the internal combustion engine, detecting An accelerator position sensor for opening the accelerator, an air flow measuring instrument for measuring the amount of air flowing through the intake passage 2 , etc.), and their output signals are input to the ECU 15 . In addition, in addition to the bypass valve 8, the fuel addition valve 9, and the glow plug 10, the ECU 15 is also connected to an in-cylinder fuel injection valve (not shown) that directly injects fuel for combustion of the internal combustion engine into the cylinder through electrical wiring. shown), these components are controlled by the ECU15.

When it is necessary to raise the temperature of the exhaust purification catalyst 4 , the ECU 15 performs a temperature raising process of raising the temperature (hereinafter referred to as "catalyst temperature") TC of the exhaust purification catalyst 4 . The temperature raising process in this embodiment is a process of raising the catalyst temperature TC to the temperature raising target temperature TCt by raising the temperature (hereinafter referred to as "inflow gas temperature") TGc of the exhaust gas flowing into the exhaust purification catalyst 4 . Here, the temperature increase target temperature TCt refers to the target temperature of the exhaust purification catalyst 4 when the temperature increase process is performed. For example, a temperature obtained by adding a predetermined margin to the activation temperature of the exhaust purification catalyst 4 can be used as the temperature increase target temperature TCt. In addition, the need to raise the temperature of the exhaust purification catalyst 4 may occur when the catalyst temperature TC is lower than the activation temperature of the exhaust purification catalyst 4 .

In the temperature raising process, the ECU 15 adds fuel to the exhaust gas from the fuel addition valve 9 and energizes the glow plug 10 to perform control to ignite the added fuel (hereinafter referred to as “fuel ignition control”). According to this fuel ignition control, since the inflow gas temperature TGc rises due to the combustion of the added fuel, the catalyst temperature TC can be appropriately raised. Here, the term "addition of fuel" in this specification refers to the fuel added to the exhaust gas from the fuel addition valve 9, and is used to distinguish it from the fuel injected from the in-cylinder fuel injection valve arranged in each cylinder for combustion of the internal combustion engine. .

Here, when other conditions are equal, the amount of increase in the inflow gas temperature TGc increases as the amount of fuel added in the fuel ignition control increases, so the amount of increase in the catalyst temperature TC also increases. However, if the amount of fuel added in the fuel ignition control increases, the temperature of the combustion gas during combustion of the added fuel will increase, resulting in an increase in the amount of smoke generated.

FIG. 2 is a diagram illustrating an example of the relationship between the glow plug peripheral gas temperature TGg and the smoke generation amount Qsm during fuel ignition control. The “gas temperature TGg around the glow plug” is the temperature of the exhaust gas flowing around the glow plug 10 . When other conditions are equal, the higher the gas temperature TGg around the glow plug becomes, the higher the combustion gas temperature becomes when the added fuel is burned. Therefore, the smoke generation amount Qsm in the fuel ignition control tends to increase as the glow plug peripheral gas temperature TGg increases.

In view of this, in the temperature raising process, the temperature of the exhaust purification catalyst 4 is raised while reducing the smoke generation amount Qsm in the fuel ignition control. Specifically, the ECU 15 executes the control of opening the bypass valve 8 so that the high-temperature exhaust gas bypassing the turbine 6 b flows into the exhaust purification catalyst 4 through the bypass passage 7 together with the fuel ignition control (hereinafter referred to as "bypass"). control").

When the bypass control is executed, part of the exhaust gas discharged from the internal combustion engine 1 flows into the bypass passage 7 from the bypass branch portion 3a, and the remaining exhaust gas flows into the turbine 6b. Inside the turbine 6b, a turbine blade (not shown) rotatably supported by a shaft is provided, and the turbine blade rotates based on the energy of the exhaust gas flowing into the turbine 6b. The rotational torque of the turbine blade is transmitted to a compressor blade (not shown) which is rotatably supported inside the compressor 6a, and the air flowing into the compressor 6a is compressed. That is, when the exhaust gas flows into the turbine 6b, part of its energy is consumed by supercharging the intake air. Therefore, the temperature of the exhaust gas after it flows out of the turbine 6b is lower than before it flows in.

On the other hand, during the bypass control, the exhaust gas passing through the bypass passage 7 bypasses the turbine 6 b and is introduced into the exhaust purification catalyst 4 while being kept at a high temperature. 3 is a map illustrating an example of the relationship between the inflow gas temperature TGc during bypass control and the fuel addition amount (hereinafter referred to as "required fuel addition amount") Fur required for fuel ignition control. Here, the higher the bypass inflow ratio Rbp during bypass control is, the higher the inflow gas temperature TGc is, and the closer the catalyst temperature TC is to the temperature increase target temperature TCt. Therefore, the higher the bypass inflow ratio Rbp in the bypass control, the lower the required fuel addition amount Fur in the fuel ignition control.

The ECU 15 executes bypass control prior to fuel ignition control. In the bypass control, the ECU 15 adjusts the opening of the bypass valve 8 so that the bypass inflow ratio Rbp is at least greater than the turbine inflow ratio Rtb (that is, becomes a value larger than 0.5). As a result, an increase in the inflow gas temperature TGc in the bypass control and a decrease in the required fuel addition amount FUr in the fuel ignition control can be facilitated. Therefore, the temperature of the combustion gas by fuel ignition control is lowered, thereby reducing the smoke generation amount Qsm.

In addition, in the present embodiment, the fuel addition valve 9 and the glow plug 10 are arranged between the turbine 6 b and the bypass confluence portion 3 b in the exhaust passage 3 . According to such a temperature raising system, the gas temperature TGg around the glow plug during fuel ignition control can be significantly lowered than a system in which the fuel addition valve 9 and the glow plug 10 are arranged on the upstream side of the turbine 6b. Accordingly, since the temperature of the combustion gas during the fuel ignition control becomes lower, the amount of smoke generation Qsm can be reduced.

Hereinafter, specific contents of the temperature raising process for the exhaust purification catalyst 4 will be described with reference to the flowchart shown in FIG. 4 . Fig. 4 is a flowchart showing a first temperature raising processing routine. This program is stored in ECU 15 in advance and is repeatedly executed at predetermined intervals. In this embodiment, the ECU 15 executing this program corresponds to the first temperature rise control means and the second temperature rise control means in the present invention.

When this routine is executed, first, in S101 , the ECU 15 judges whether there is a need to raise the temperature of the exhaust purification catalyst 4 . Specifically, the catalyst temperature TC is estimated from the output signal of the first temperature sensor 11, and when the estimated temperature is lower than the activation temperature of the exhaust purification catalyst 4 (NOx catalyst), it is determined that the temperature needs to be raised. In this step, when it is judged that there is a need to raise the temperature, it is judged that it is necessary to perform the temperature raising process on the exhaust purification catalyst 4, so the process proceeds to step S102. On the other hand, when it is judged that there is no need to raise the temperature of the exhaust purification catalyst 4, the ECU 15 temporarily skips this routine.

In step S102, ECU 15 executes bypass control. Specifically, the ECU 15 calculates the target value of the bypass inflow ratio Rbp in the bypass control based on the map shown in FIG. 3 so that the required fuel addition amount Fur does not exceed the upper limit fuel addition amount FUlm. The upper limit fuel addition amount FUlm is a preset upper limit value of the fuel addition amount to suppress the smoke generation amount Qsm during fuel ignition control within an allowable range, and can be preset based on empirical rules such as experiments. Then, the ECU 15 controls the opening degree of the bypass valve 8 so that the bypass inflow ratio Rbp becomes the calculated target value. For example, in order to increase the bypass inflow ratio Rbp as much as possible during bypass control, the opening degree of the bypass valve 8 may be increased to the full opening degree (maximum opening degree). As a result, the increase in the inflow gas temperature TGc in the bypass control and the reduction in the required fuel addition amount FUr in the fuel ignition control can be accelerated as much as possible. The ECU 15 proceeds to step S103 after the processing of this step is completed.

In step S103 , the ECU 15 substitutes the bypass inflow ratio Rbp in the bypass control into the map shown in FIG. 3 . Then, the ECU 15 reads the required fuel addition amount FUr corresponding to the bypass inflow ratio Rbp, and calculates the fuel addition amount to be added by the fuel addition valve 9 during the fuel ignition control. In the next step S104, the ECU 15 executes fuel ignition control. That is, the ECU 15 causes the fuel addition valve 9 to add fuel to the low-temperature exhaust gas flowing out of the turbine 6b. The fuel addition amount at this time may be the value calculated in step S103. Then, the ECU 15 ignites the glow plug 10 when the mixed gas mixed with the fuel added by the fuel addition valve 9 reaches the vicinity of the glow plug 10 . As a result, the inflow gas temperature TGc further rises due to the added fuel combustion, and the catalyst temperature TC rises to the temperature rise target temperature TCt. After the processing of this step is completed, the ECU 15 temporarily jumps out of this routine.

As described above, according to the temperature raising system of the exhaust gas purification catalyst in the present embodiment, when the additional fuel is combusted in the fuel ignition control, it is possible to reduce the generation of smoke.

<Example 2>

Next, a second example among the embodiments of the present invention will be described. The schematic structure of the internal combustion engine and its intake and exhaust system to which the temperature raising system in this embodiment is applied is the same as that shown in FIG. 1 . Hereinafter, a description will be given centering on the characteristic parts of the temperature raising system of the present embodiment. In this embodiment, the bypass valve 8 is controlled so that the turbine inflow ratio Rtb is larger than the bypass inflow ratio Rbp when the fuel ignition control is executed, and the bypass valve 8 is controlled so that the bypass inflow ratio Rbp after the fuel ignition control is executed is larger than the turbine inflow ratio Rtb. The inflow ratio Rtb is large.

Fig. 5 is a flowchart showing a second temperature raising processing routine. This program is stored in ECU 15 in advance and is repeatedly executed at predetermined intervals. In this embodiment, the ECU 15 executing this program corresponds to the first temperature rise control means and the second temperature rise control means in the present invention. In this program, steps that perform the same processing as in FIG. 4 are assigned the same reference numerals, and descriptions thereof are omitted.

In step S201, the ECU 15 operates the bypass valve 8 in the valve-closing direction up to the target opening degree Diga during ignition control. The ignition control target opening Diga is such that the turbine inflow ratio Rtb is larger than the bypass inflow ratio Rbp. When the opening degree of the bypass valve 8 is decreased from the opening degree during bypass control to the target opening degree Diga during ignition control, the amount of exhaust gas passing through the glow plug 10 per unit time (hereinafter referred to as "glow plug passing gas amount") increases. . For example, 0 may be used as the target opening Diga during ignition control. At this time, the bypass valve 8 is completely closed, and the cross-sectional flow area of the bypass passage 7 is zero. As a result, the bypass inflow ratio Rbp becomes 0, and the turbine inflow ratio Rtb becomes 1.

In the next step S104, the ECU 15 executes fuel ignition control. That is, since the fuel ignition control is executed in a state where the amount of gas passing through the glow plug is increased compared with the bypass control, the heat capacity of the exhaust gas flowing around the glow plug 10 increases. As a result, the temperature of the combustion gas during the fuel ignition control is lowered, and the smoke generation amount Qsm can be reduced. In addition, if the amount of gas passing through the glow plug is increased, the amount of oxygen consumed during combustion ignition control increases, so that the generation of smoke can be appropriately suppressed.

In step S202, the ECU 15 operates the bypass valve 8 in the valve-opening direction to the post-ignition control target opening degree Digb. The post-ignition control target opening Digb is the target opening of the bypass valve 8 after the fuel ignition control is executed, and is an opening at which the bypass inflow ratio Rbp can be made larger than the turbine inflow ratio Rtb. Therefore, the target opening degree Digb after ignition control is set to be on the ON side compared with the target opening degree Diga during ignition control (Diga<Digb). Through the temperature raising process in this embodiment, the bypass inflow ratio Rbp is increased compared to the fuel ignition control. Thereby, more exhaust gas maintained at a high temperature can flow into the exhaust purification catalyst 4, and the temperature rise of the exhaust purification catalyst 4 can be further accelerated. After the processing of this step is completed, the ECU 15 temporarily jumps out of this routine.

<Example 3>

Next, a third example among the embodiments of the present invention will be described. The schematic structure of the internal combustion engine and its intake and exhaust system to which the temperature raising system in this embodiment is applied is the same as that shown in FIG. 1 . Fig. 6 is a flowchart showing a third temperature raising processing routine. This program is stored in ECU 15 in advance and is repeatedly executed at predetermined intervals. In this program, steps that perform the same processing as in FIG. 5 are assigned the same reference numerals, and descriptions thereof are omitted.

If the execution of the fuel ignition control ends in step S104, the ECU 15 proceeds to step S301. In step S301 , the ECU 15 reads the output signals of the second temperature sensor 12 and the third temperature sensor 13 . Then, the ECU 15 estimates the gas temperature TGg around the glow plug from the output signal of the second temperature sensor 12, and estimates the temperature of the exhaust gas in the bypass passage 7 based on the output signal of the third temperature sensor 13 (hereinafter referred to as “bypass gas temperature TGg”). temperature") TGbp.

In step S302, the ECU 15 determines whether or not the bypass gas temperature TGbp is higher than the glow plug peripheral gas temperature TGg. Then, when it is determined that the bypass gas temperature TGbp is higher than the glow plug peripheral gas temperature TGg (TGbp>TGg), the process proceeds to step S202. That is, the ECU 15 operates the bypass valve 8 in the valve-opening direction up to the post-ignition control target opening degree Digb. On the other hand, when it is determined that the bypass gas temperature TGbp is equal to or less than the glow plug peripheral gas temperature TGg (TGbp≦TGg), the ECU 15 returns to the process of step S301. That is, the processes of steps S301 and S302 are repeated until it is determined that the bypass gas temperature TGbp is higher than the glow plug peripheral gas temperature TGg.

If fuel ignition control is executed, components (exhaust pipes) constituting the exhaust passage are heated by heat generated in this fuel ignition control. Therefore, it is considered that after execution of the fuel ignition control, the glow plug peripheral gas temperature TGg is maintained at a higher temperature than the bypass gas temperature TGbp. In view of this, in the temperature raising process of the present embodiment, the bypass valve 8 is maintained at the ignition control target opening until it is judged that increasing the bypass inflow ratio Rbp can raise the catalyst temperature TC compared to the fuel ignition control execution time. Degree Diga. Accordingly, it is possible to more efficiently increase the temperature of the exhaust purification catalyst 4 after execution of the fuel ignition control.

In addition, as a modified example of the above control, the ECU 15 may estimate the amount of gas passing through the glow plug after execution of the fuel ignition control and the amount of gas passing through the bypass passage 7 (hereinafter referred to as "the amount of gas passing through the bypass passage"). This amount of gas is used to estimate the timing at which the bypass gas temperature TGbp exceeds the glow plug peripheral gas temperature TGg. Then, the ECU 15 may switch the opening degree of the bypass valve 8 to the post-ignition control target opening degree Digb at the timing when the bypass gas temperature TGbp exceeds the glow plug peripheral gas temperature TGg.

<Example 4>

Next, a fourth example among the embodiments of the present invention will be described. Fig. 7 is a diagram showing a schematic configuration of an internal combustion engine to which the temperature raising system in this embodiment and its intake and exhaust systems are applied. Components common to those in FIG. 1 are given the same reference numerals. Between the glow plug 10 and the bypass confluence portion 3 b in the exhaust passage 3 of the present embodiment, a reforming catalyst 17 for reforming fuel contained in the inflowing exhaust gas is disposed.

As described above, since the DPNR catalyst is used as the exhaust purification catalyst 4, a NOx catalyst is included. Since there is an upper limit to the NOx storage capacity of the NOx catalyst, the ECU 15 performs control to reduce and purify NOx before the NOx storage amount in the NOx catalyst reaches the storage capacity. Specifically, the ECU 15 performs fuel supply control in which unburned fuel as a reducing agent for reducing NOx is added from the fuel addition valve 9 and supplied to the NOx catalyst included in the exhaust purification catalyst 4 .

However, in order to promote the reduction reaction of NOx in the NOx catalyst, it is necessary that the NOx catalyst is in an active state. Therefore, when the temperature of the NOx catalyst is lower than the activation temperature, it is necessary to first perform the temperature raising process and then perform the fuel supply control. Hereinafter, specific processing contents executed by the ECU 15 when shifting from the temperature raising processing to the fuel supply control will be described. Fig. 8 is a flowchart showing a fourth temperature raising processing routine. This routine is stored in ECU 15 in advance and is repeated at predetermined intervals. In this program, steps that perform the same processing as in FIG. 5 are assigned the same reference numerals, and descriptions thereof are omitted.

If the execution of the fuel ignition control ends in step S104, the ECU 15 proceeds to step S401. In step S401, the ECU 15 determines whether or not it is necessary to execute fuel supply control. For example, the ECU 15 can estimate the NOx storage amount of the NOx catalyst, and generate the need for execution when the storage amount exceeds a predetermined value. In this step, when the ECU 15 determines that it is necessary to execute the fuel supply control, the process proceeds to step S402. On the other hand, when it is judged that there is no need to execute the fuel supply control, the process proceeds to step S202, and the bypass valve 8 is operated in the valve opening direction from the target opening degree Diga during ignition control to the target opening degree Digb after ignition control.

In step S402, the ECU 15 operates the bypass valve 8 in the valve opening direction from the target opening degree Diga during ignition control to the target opening degree Digc during fuel supply control. The target opening degree Digc during fuel supply control is a target opening degree of the bypass valve 8 during fuel supply control. The target opening degree Digc during fuel supply control in this embodiment is set to be closer to the closing side than the target opening degree Digb after ignition control (Digb>Digc).

Then, in step S403, the ECU 15 executes fuel supply control by causing the fuel addition valve 9 to add a predetermined amount of fuel to the exhaust gas. Since the execution of the fuel ignition control has ended, the reforming catalyst 17 is surely brought into an active state. Therefore, the added fuel from the fuel added valve 9 is partially oxidized based on the catalyst function of the reforming catalyst 17 . By supplying the fuel thus reformed by the reforming catalyst 17 to the NOx catalyst, the reduction reaction of NOx stored in the NOx catalyst can be favorably promoted. When the execution of the fuel supply control is completed, the ECU 15 operates the bypass valve 8 in the opening direction from the target opening degree Digc during fuel supply control to the target opening degree Digb after ignition control in step S404. After the processing of this step is completed, temporarily exit this program.

In addition, the target opening degree Digc during fuel supply control may be made to coincide with the target opening degree Diga during ignition control during fuel ignition control. In this case, in step S402, the opening degree of the bypass valve 8 is maintained at the target opening degree Diga at the time of ignition control. Then, in step S404, the opening degree of the bypass valve 8 is changed from the target opening degree Diga during ignition control to the target opening degree Digb after ignition control. In addition, the fuel supply control in this embodiment is performed not only at the time of reducing NOx stored in the NOx catalyst, but also at the time of recovering the sulfur poisoning of the NOx catalyst.

The present embodiment described above is merely an example for describing the present invention, and various changes can be added without departing from the scope of the present invention. In addition, the configurations and controls described in Embodiments 1 to 4 can be combined as much as possible.

Explanation of Reference Signs: 1-internal combustion engine, 3-intake passage, 3a-bypass branch, 3b-bypass confluence, 4-exhaust gas purification catalyst, 6-turbocharger, 6b-turbine, 7-bypass Passage, 8-bypass valve, 9-fuel adding valve, 10-glow plug, 15-ECU.

Claims (2)

1. the temperature elevation system of an exhaust emission control catalyst, is characterized in that, possesses:

Turbine, it is arranged on the exhaust passageway of internal-combustion engine;

Exhaust emission control catalyst, it is arranged on the part of the above-mentioned turbine downstream of ratio in above-mentioned exhaust passageway;

The bypass path, it is by the above-mentioned turbine in above-mentioned exhaust passageway and the part between above-mentioned exhaust emission control catalyst and the part by upstream side couples together than this turbine;

Fuel addition valve, it is arranged on downstream side joint that exhaust passageway in above-mentioned exhaust passageway, above-mentioned is connected with above-mentioned bypass path and the part between above-mentioned turbine, for the waste gas to flowing through exhaust passageway, adds fuel;

Ignition mechanism, it is arranged on above-mentioned downstream side joint in above-mentioned exhaust passageway and the part between above-mentioned turbine, for the interpolation fuel to utilizing above-mentioned fuel addition valve to add, is lighted a fire;

The 1st temperature rise control mechanism, when the above-mentioned exhaust emission control catalyst of needs heats up, the 1st temperature rise control mechanism flow in above-mentioned exhaust emission control catalyst the waste gas of walking around above-mentioned turbine via above-mentioned bypass path; And

The 2nd temperature rise control mechanism, when the above-mentioned exhaust emission control catalyst of needs heats up, the 2nd temperature rise control mechanism is carried out fuel ignition and is controlled, wherein, it is to make above-mentioned fuel addition valve add fuel to the waste gas flowed out from above-mentioned turbine that this fuel ignition is controlled, and the control that above-mentioned ignition mechanism is lighted a fire to adding fuel.

2. the temperature elevation system of exhaust emission control catalyst according to claim 1, is characterized in that,

Also possesses the ratio of inflow change device, this inflow ratio change device can flow into ratio and turbine to bypass and flow into ratio and changed, wherein, it is to flow into the exhausted air quantity of above-mentioned bypass path and the ratio of all waste gases amount of discharging from above-mentioned internal-combustion engine that this bypass flows into ratio, it is to flow into the exhausted air quantity of above-mentioned turbine and the ratio of this all waste gases amount that this turbine flows into ratio

Above-mentioned the 1st temperature rise control mechanism control above-mentioned inflow ratio change device make turbine when carrying out fuel ignition and controlling flow into ratio to flow into ratio than bypass large, and controlling this inflows ratio change device, to make the bypass of carrying out after fuel ignition is controlled flow into ratio larger than turbine inflow ratio.

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